Most soils in the Northeast of Thailand
are sandy in texture. They are poor both in physical and chemical properties. Saline soils
currently occupy an area of approximately 17% of the region and are increasing annually. These saline sandy soil
can be detrimental to plant growth and result in low yields, this being mainly due to low fertility, high
soluble salts and low water holding capacity. To grow crops successfully, these
soils must be
improve. The objective of this study is to elucidate the effect of organic and
inorganic fertilizers on yield and quality of ruzi (Brachiaria ruziziensis) grass
on saline sandy soils of the Northeast Thailand.

Experiment design was factorial
in RCBD with 3 replications. Factors were 3 rates of chicken manure (0, 1.87 and 3.75 t/ha), 2 rates of rice husk (0 and 5
t/ha) and 3 rates of 15-15-15, inorganic fertilizer (0, 156 and 312 kg/ha). Ruzi grass seedlings were transplanted in to 2
× 3 m
plot on a Typic Natraqualfs soil at a 30 × 30 cm
spacing. Both fresh and dry weight of grass was measured at harvest. For dry
weight, increasing rates of manure resulted in an increase in
yield. These was significantly different between control and
3.75 t/ha. Rice husk also gave significant dry weight differences between
control and 5 t/ha rate. For the 15-15-15, inorganic
fertilizer, the application at 156 kg/ha increased dry weight significantly
from control. There was a significant interaction between rice husk and
inorganic fertilizer. It was concluded that chicken manure at 3.75 t/ha
together with rice husk at 5 t/ha and fertilizer at 156 kg/ha was the best
combination rate to give highest grass dry weight under this saline and sandy
condition. Grass quality such as crude protein, neutral
detergent fiber and acid detergent fiber were analysed. Soil chemical
properties such as pH, EC, OM, total
N, available P, exch, K and exch, Na were also analysed before and after the
experiment.

Introduction

Most soils in the northeast are
sandy in texture. They
are poor in physical, chemical and biological properties. Saline soils currently occupy an area of approximately 17% of the region and are increasing
annually. Most saline soils are also
sandy, these saline sandy soils can
be deleterious to plants and result in low yields, due to low fertility,
high soluble salts especially sodium
chloride, low water holding capacity and low cation exchange capacity.
To grow crops successfully, these soils must be improve. The objective of this
study is to elucidate the effect of organic
and inorganic fertilizers on yield and quality of ruzi g_ass as well as the
changes in soil properties used in the experiment.

Materials
and Methods

Experiment design was factorial
in RCBD with 3 replications. Factors were 3 rates of chicken manure (0, 1.87 and 3.75 t/ha), 2 rates of rice husk (0 and 5
t/ha) and 3 rates of 15-15-15, inorganic fertilizer (0, 156 and 312 kg/ha).
Ruzi grass seedlings were transplanted into
2 × 3 m plot of Kula Ronghai series soil (Ki, Typic
Natraqualfs) with 30 × 30 cm spacing. Both fresh weight and dry weight of grass were measured
as well as grass quality. Soil properties before
and after the experiment was also measured.

Results and Discussion

Some properties of Kula Ronghai series soil (Ki, fine-loamy, mixed, active, isohyperthermic,
Typic Natraqualfs) before the experiment are shown in Table 1. This soil is slightly saline soil with
high soil reaction (pH) low in plant
nutrients but high in sodium and sandy in texture.

Some properties of chicken manure and rice husk used in the experiment
are shown in Table 2. Chicken manure is slightly basic with a pH 8.4, has a
high electrical conductivity, organic matter and available plant nutrients relative
to other organic fertilizers. Rice husk got very low electrical con­ductivity and was also low in organic matter and
other nutrients.

The effect of chicken manure, rice husk a_d chemical fertilizer on fresh weight of Ruzi grass
were shown in Table 3. There was highly significantly different between the different levels of manure,
rice husk and chemical fertilizers,
the interaction took place only for
rice husk and chemical fertilizer.

Table 4 also clearly shows the
effect of chicken manure, rice husk and
chemical fertilizer on fresh weight of Ruzi
grass. Manure at both rates gave higher fresh weights that were
significantly different from the control.
Treatments receiving rice husk at a rate of 5 t/ha also gave significantly different from control and similarly
chemical fertilizer also gave higher fresh weights
that were significantly from control.

The effect of chicken manure, rice husk and chemical fertilizer on dry weight of Ruzi grass
were shown in Table 5, there was highly significantly different between the different levels of manure,
rice husk and chemical fertilizer, again the interaction took place only for
rice husk and chemical fertilizer.

The effect of chicken manure, rice husk and chemical
fertilizer on dry weight of Ruzi grass are shown
in Table 6. There was no significant difference between manure rate at 0 and
1.87 t/ha, 1.87 t/ha and 3.75 t/ha
but there was a significantly different between 0 and 3.75 t/ha. Rice
husk at 5 t/ha also gave significantly
different on dry weight basis. Chemical fertilizer at 156 kg/ha gave higher and significantly different dry weight as well as at 312 kg/ha from
the control.

It could be concluded at this
point that the best combination
rate for manure, rice husk and chemical fertilizer for grass fresh weight was 1.87 t/ha, 5 t/ha and 156 kg/ha while for grass dry
weight was 3.75 t/ha, 5
t/ha and 156 kg/ha respectively. In other word, to increase dry weight
significantly, more manure was needed.

The effect of chicken manure rice husk and chemical fertilizer on Ruzi grass quality were shown in Table 7.
Manure at 3.75 t/ha with 312 kg/ha of chemical
fertilizer gave highest crude protein whether with or without rice husk. For neutral detergent fiber the values from different treatments gave similar
result but manure at 3.75 t/ha with or without rice husk at 5 t/ha gave the highest value for neutral
detergent fiber. Manure at 3.75 t/ha with rice husk at 5 t/ha and 312 kg/ha of chemical fertilizer gave the lowest
value needed for acid detergent fiber.

The effect of chicken manure, rice husk and chemical fertilizer on soil properties before and
after the experiment were shown in Table 8. It seems to be that soil pH was increased after added manure,
rice husk and chemical fertilizer. Electrical conductivity and Na of soil were also increased, this could be
the result from more ions lefted from the experiment as well as more Na from the capillary action of
brine in the soil.
Organic matter as well as N, P and K after the experiment were also higher. This could be the
residual effect of
chemical fertilizer. When comparing these values with control after the experiment. The control treatment was higher in electrical conductivity and very high Na, while lower in other plant
nutrients. This suggested that to grow crop successfully and to maintain
soil fertility, organic materials as well as chemical
fertilizer should be applied at proper rates.

Table 8. Total effect of chicken manure, rice husk
and chemical fertilizer on soil properties before and after the experiment

pH (1:1, H2O)

ECe(dS/m)

OM
(%)

Total N

Available P Exch. K

Exch. Na

Texture

(ppm)

Before**
After**
Control (after)

9.8
10.2
10.4

2.35
3.15
3.60

0.19
0.28
0.02

115
175
16

22
122
7 40

1,270

2,128

Same

Same

Conclusions

Saline sandy soils which are poor in physical and
chemical properties as well as low in fertility
can be used for pasture in the northeast, if managed correctly. The objective
of this study is to elucidate the
effect of organic and inorganic fertilizer on yield and quality of ruzi
grass grown on saline sandy soils of the northeast. Factors involved were 3
rates of chicken manure, 2 rates of rice husk and 3 rates of inorganic fertilizer. For dry weight of ruzi grass,
increasing rates of manure could increase yield. There was significantly
different between control and 3.75 t/ha of manure rate. Rice husk also
gave significant dry weight differences
between control and 5 t/ha rate. For
the 15-15-15, inorganic fertilizer the application
at 156 kg/ha could increase dry weight of grass
significantly from control. It could be concluded that manure at 3.75 t/ha with
rice husk at 5 t/ha and fertilizer at 156 kg/ha was the best combination rate to give the
highest dry weight of grass under the studied condition but for fresh weight lower rate of
manure seem to be better.

References

Phaikaew, C. and Pholsen, P. (1993). Ruzi grass
(Brachiaria ruziziensis) seed
production and research in Thailand.
Processing of FAO 3rd
Meeting of Regional Working Group on
Grazing and Feed Resources of Southeast Asia. Thailand:
Khon Kaen.

Richards L.A.
(1954). Diagnosis and Improvement of Saline and Alkali Soil. Agriculture
Handbook No. 60. United States Salinity: United States Depart_ent of Agriculture.

The majority of soils in Northeast Thailand are of low fertility and acidic to
depth. Moreover 17% of cultivated soils in the region are affected by salinity that has its
origin in saline groundwater that has risen to within 1 m of the soil surface.
Traditional rice growing techniques are not well adapted to these kinds of soil constraints
that often results in the abandonment of entire fields or areas within fields
due to salinization. A study was undertaken to determine the effects of rice cropping on
these saline sandy soil with respect to changes in the geochemical attributes of the soil
solution and their consequences on soil conservation.

An accurate assessment of
geochemical changes and associated mechanisms, including the effects of
reducing conditions on soil solution composition, is difficult to undertake
under field conditions. Thus we established a laboratory experiment where
conditions similar to those in the field could be simulated. Four undisturbed
soil columns of 50 cm in height and 24.5 cm in diameter we collected from Northeast Thailand,
two of which were saline (S) and two non-saline
(NS). Rice was transplanted into one of the columns from each of soil salinity types. The
columns were designed to continuously monitor pH, Eh and the chemical
composition of solution at three depths namely -7, -24, -40 cm. An increase in
pH was observed within the acidic NS column with the pH rising to almost neutrality
within the surface horizon. This increase in pH is controlled by iron reduction. At
the second depth interval (i.e. -24 cm) manganese reduction control changes in pH along with changes in the
partial pressure of CO2. The highest increase in pH was measured in
the NS columns cropped with rice whilst the smallest increase in pH was
observed in the un-cropped S soil. On these sandy soils the production of
rice using farmers practices contributes to increases in pH and temporarily
controls the expansion of salinity by diluting the salt above the soil.
Continued traditional rice cropping contributes
to limiting the expansion of degradation on these soils.

Introduction

Soil salinisation is a global problem that is estimated to affect 6.5% of the earth’s soil
surface is (Cheverry et al. 1998). In Northeast
Thailand, problems of salinisation and soil degradation have attained an important level (Kohyama et al.,
1993). The soils of the region soils are sandy (Mitsuchi et al., 1986;
Yuvaniyama, 2001), with very low nutrient supplying
capacity (Ragland and Boonpuckake, 1988) and low organic matter (OM) contents
(Arunin1986). Around 17% of this
area’s soils are affected and a further
108,000 km2 which is more than twice the size of Switzerland are potentially at risk
by the same phenomenon. Upland deforestation leading to a rise of the saline watertables has been the main cause of
the increase in soil salinisation (Williamson et al., 1989). This
problem is of increasing importance to national stakeholders concerned
over their continued use of these soils for agricultural. A decrease in rice
production yield due to the occurrence of saline patches could have serious affects on this area’s ability to
satisfy the rising food demands of its increasing population (Fukui, 1991; Kono, 1991). Moreover, rice cropping
forms a distinct cultural element in communities of northeast that has
significant implications on the
socio-economic status of the region (Formoso
et al., 1997). Hence a decline in rice yields would have serious
consequences.

Salinity issues have been studied for many years in this region of Thailand
(Arunin, 1984), (Brinkman et al., 1977).
However, there are still unanswered questions
on the dynamics of saline patches and the respective soil development. It was therefore decided to study the
impact that rice cropping has on these impoverished,
sometimes acidic soils that are subject to salinisation. The first
results of this study show significant differences in terms of acidity, notably
during the dry season, between the saline and non-saline zones. In previous studies Grunberger (2002) observes saline zones having a neutral pH of
6.5-7 and non-saline having a pH of 4.5-5. The discrepancy between pH levels would suggest a modification in
behaviour between saline and non-saline patches situated in close
proximity to one another (a few metres) on soils of identical origin.
Therefore, an evaluation was undertaken
using undisturbed columns collected
from cultivated and non-cultivated soil with the objective of identifying the effects of traditional rice cropping on soil geochemistry notably the
role o plants and salinisation. Since pH is an importan indicator of soil quality, variations in pH and Eh
are studied in the first months following submersion.

Methods

Experiments were conducted on
cultivated plots in
Pra Yuhn, near Khon Kaen, Northeast Thailand
(16º21′12.744 North
and 102º36′29.8′′ East).

In the saline patches the
exchangeable complex is dominated by
sodium. The region has a tropical Savannah
climate with a mean annual rainfall of 1,200
mm from May to October. Evaporation is greater than precipitation, except at the height of the rainy season from July to September (Bolomey, 2002).
Soil is regularly saturated by solutions
of NaCl as the water table rises and conductivity has an average value
of 20 dS m-1 at a pH of 6.82.
The water table is near the soil
surface at the end of the rainy season and draws down by 2 m in the dry
season.

The study was conducted in the
laboratory for optimal
control of conditions and ease of monitoring. Four undisturbed soil columns (47 cm high and
24.5 cm in diameter)
were tested; two from within the saline patch and two from outside. Rice was planted on one
column from each of the two sites. Thus four distinct types were possible;
non-saline/non-cultivated C4 (NS NC),
non-saline/cultivated C3 (NS C), saline/non-cultivated
C1 (S NC)
and saline/cultivated C2 (S C).

Efforts were made to reproduce
field conditions and ensure that all
interventions and measures were conducted in the same
way on each column. Measurement and
sampling equipment was installed to control the water flow, measure pH
and Eh and to study chemical evolution of
soil solution. D_fferent measuring equipment was installed at three
levels; at 7 cm, less than 24 cm and at 41
cm from surface (Figure 1).

Figure 1. Diagram of a soil column with instrumentation installed to monitoe pH, Eh, chemical composition
of the solution, at three depths

The soil has a sandy loam
texture (Grunberger, 2002),
less than 10% clay content and low, superficial levels of organic matter (OM)
(Table 1). The soil was classified as an
Ultisols (Roi Et series in the Thai classification
system) having a low cation exchange capacity,
less than 5 cmolc kg -1 of
soil (Table1).

After a week’s saturation, the
soil surface of the columns was flooded
to a predetermined level using a Marriotte
device. Deionised water was used so as to simulate rainwater that under
natural conditions irrigates the field plots. Five rice plants were transplanted in two columns to simulate a tuft of
plants in the field. Weekly samples
of water were taken and analysed. The
pH and Eh were measured twice a week, always at the same time.

Studies on reduction in saturated soil and evolution of pH have demonstrated the important
roles of microorganisms, certain
minerals such as iron and manganese
hydroxides and also the partial pressure of CO2 (p CO2) (Berthelin, 1998; Ponnamperuma, 1972;
Zhi-Guang, 1985; Sumner, 2000).

Analysis for this study is based
on two important equations
that characterise the transformation of iron and of manganese when undergoing oxidation and reduction.

Equation 1 shows the stochiometry of the reaction
between iron hydroxides (i.e. goethite dissolution)
and protons that result in an increase in pH (Chamayou, 1989).

where the reduction of Fe (III) to Fe (II) consumes H+
and causes an
increase in pH. Similarly, as for the iron, the reduction of manganese consumes protons (Sigg et al.,
1992).

Results

All soil samples show an initial acid pH (Figure 2). This is followed by a rapid reduction in
the Eh of the soil profile, reaching
as low as -0.35V for the non-saline/cultivated
soil column (C3 NS C). For this column
the kinetics of reactions was extremely rapid. The pH and Eh of the saline samples (S NC
and S C) developed less rapidly. The level of salinity can influence
microbial activity by slowing down the development
of populations thereby influencing the reduction
processes within the soil profile. Iron plays the major role in the in these reaction in the surface horizons
of the soil profile, where the presence of Fe (II) is found (Figure 3). This is
partly caused by a reduction reaction of Fe
(III) to Fe (II) (equation 1).

The presence of ferrous iron is
demonstrated by the results of chemical analysis in Table 2.

For the deeper soil layers (24 to
41 cm) the four columns have higher potential for Eh than the surface layer.

Manganese reduction tends to
occur before iron in
the order of reaction. It appears in the transition phase of soil that is changing
from the oxidised to the reduced
state (Sumner, 2000). However, only high levels of manganese in the soil
profile can produce a significant effect.
The abundance of manganese in this soil can be confirmed, due to the
presence of nodules of manganese when the
soil was sieved. It was also found
when analysing the soil solution (Table 2). This confirms that in this soil, manganese is mobilised and precipitates as shown by the oxydoreduction
of the soil. As for the iron, the reduction of manganese consumes protons (Equation 2). The influence of Mn
is demnonstrated in the depth layers
of >24 cm, and is presented in
Figure 4. A strong correlation between the presence of Mn in solution
and pH development is clearly evident. These observations can be used to construct phase equilibrium diagrams for the
different forms of Mn that are present in solution and solid phases, namely, MnO2 and Mn2+
for the profiles at the 24 cm depth
interval (Figure 5). Equilibrium between solid and solution phases depends on the log of activity for Mn2+
in so_l solution and is written in the following way (Sigget al., 1992):

Figure 2. Soil solutions pH development over time
at a depth of 7 cm for the four undisturbed
columns

Figure 3. Relationship
between pH and pe for soil solutions, of the
four columns within the 7 cm layer

Table 2. Soil solutions composition

Date

Al

Ca

Fe

Mg

Mn

Na

Cl

EC mS/cm

Calculated alkalinity

Analyse alkalinity

me/L

me/L

me/L

me/L

me/L

me/L

me/L

me/L

me/L

C1 S NC-7cm

22-April

0.04

0.09

0.04

0.86

0.00

2.25

0.98

0.36

1.1

1.9

25 April

0.11

0.22

0.17

0.18

0.01

6.60

4.13

0.67

2.9

29 April

0.56

0.64

0.19

0.50

0.01

13.93

13.05

1.58

1.0

06 May

0.97

0.25

0.41

0.11

0.03

8.62

4.06

0.75

5.6

4.9

13 May

0.67

0.25

0.33

0.07

0.03

8.60

3.54

0.96

6.1

6.4

C2 S C-7cm

22-April

0.01

0.31

0.22

0.39

0.01

15.23

5.69

1.61

10.2

12.9

25 April

0.00

0.43

0.17

0.55

0.01

16.64

3.74

2.00

13.3

14.4

29 April

0.00

0.49

0.11

0.48

0.01

15.99

3.64

1.06

12.7

14.9

06 May

0.00

1.02

0.32

0.44

0.04

11.98

2.53

1.32

10.5

12.9

13 May

0.00

1.46

0.67

0.32

0.07

5.84

1.16

0.81

6.4

C3 NS C-7cm

22-April

0.00

0.16

0.08

1.20

0.01

4.99

3.46

0.68

0.6

25 April

0.00

0.32

0.36

0.84

0.07

5.98

1.26

0.77

4.4

5.4

29 April

0.00

0.85

1.28

1.28

0.26

8.16

0.93

1.00

9.6

10.4

06 May

0.00

1.87

0.94

1.13

0.59

9.20

0.71

1.13

12.8

13 May

0.00

2.35

0.58

0.76

0.75

9.38

0.63

1.24

12.7

11.9

C4 NS C-7cm

15 April

0.01

0.08

0.00

0.33

0.00

2.86

1.71

0.42

-0.1

22-April

0.30

0.25

0.09

0.35

0.00

7.76

6.62

0.88

1.6

25 April

0.03

0.06

0.15

0.80

0.00

2.98

0.68

0.42

2.1

2.9

29 April

0.02

0.19

0.54

0.87

0.02

4.54

0.55

0.44

4.6

5.4

06 May

0.01

0.64

1.95

0.69

0.11

6.60

0.52

0.81

8.9

7.9

13 May

0.00

1.10

3.17

0.42

0.20

6.91

0.51

0.80

11.3

8.9

Irrigation

0.04

0.01

0.01

0.00

0.00

0.17

0.21

0.03

0.0

Water

Figure 4. Relationship between the Fe, Mn and pH with time in soil solution from the 24 cm depth
interval in treatment C3 C NS

Using the Phreeqc simulation
model (Parkhurst et
al., 1999), the
activity of Mn2+ was calculated for the different soil solutions.

Figure 5.
Relationship between pe- pH and the equi­librium
line between MnO2 and Mn2+ at 24 cm depth interval
for all columns

Figure 5, presents the phase diagram for solutions collected from the 24 cm depth interval
and demonstrates the influence of
reduced conditions on the presence of
MnO2 and Mn2+. This is probably the mechanism controlling the pH and pe of these
soils. Alkalinity and the partial
pressure of CO2 interact and control pH. In a closed system, if the pCO2 increases, the
pH diminishes. If however, in this confined medium,
the pCO2 equilibrates with atmosphere after reoxydation, pH will rise (Bourrié, 1978).

In this study, using the
Phreeqc model, partial pressure of CO2 was calculated near the soil
surface where alkalinity was measured (Figure 6). The pCO2 values do
not differ with changes in soil salinity. They have values of around 1000 times
higher than pCO2 atmospheric values, which is 10-3.5atmosphere.
Only the C1 S NC column differs, by having a
lower pCO2, closer to the atmosphere’s and less alkalinity for this
profile. An empirical relation exists which, based on the partial pCO2
pressure, allows the pH of an iron rich, submersed soil to be calculated;

Figure 6. Log of the
partial pressure of CO2 of surface laye for all columns

This
relation was derived using measurements made in the field and laboratory. This
equation was applied to this study’s measurements from soil surface (Figure 7).

Figure 7. Relationship between predicted pH and the logpCO2

The
relation could be applied to the data of this study. The small differences
observed between measured and predicted was probably due to the abundance of
manganese in soil and its affect on the control of pH. Subsequent measures made
in the field after this first experiment, show similar results on the
controlling influence of pH.

Conclusions

In
the four soil columns saline, non-saline, with or without plants, pH values of
soil solutions converge towards neutrality. The
reduction dynamics and pH evolution are related to the availability of carbon
provided around the rice roots, to feed the reductive microbial populations.
The pH of the soil has an acid tendency before reduction, which changes towards
neutrality under the influence of iron and manganese and assures more
favourable conditions for the development of rice plants.

The
differences of pH values during submerged and dry conditions are important.
These cyclic evolutions, which follow the seasons, cannot perhaps bring a
return to initial state but may produce a differentiation of pH values. The
dissolution of salt through the maintenance of submergence by fresh water on
the surface of the rice crop, produces favourable conditions for plant
development and rapidly enables reduction to take place. The effect of contact
from the rising saline water table under pressure, (Maeght et al., 2005)
can also be reduced by dilution in the layer of fresh water.

Traditional
rice growing on poor, sandy soil can contribute to temporary pH improvements in
soil by rapidly bringing about reduction in the soil surface. It can also
assist, during submergence, in controlling the expansion of salinity, by
diluting the influx of the rising saline water table in paddy fields. Extensive
soil degradation of these impoverished soils can therefore be limited by
continuing these traditional rice-cropping me_hods and in the absence of
alternative solutions, should be strongly encouraged.

References

Arunin S., 1984 - Characteristics and management of
salt-affected soils in the Northeast of Thailand. Ecology and management of
problem soils in asia. 336.